Method for sintering to be sintered material

ABSTRACT

A METHOD FOR SINTERING THE TO-BE-SINTERED MATERIAL CARRIED ON THE MOVING FIRE GRATE WHILE A FORCED DRAUGHT IS GIVEN DOWNWARD THERETO, SO AS TO OBTAIN A DURABLE SURFACE OF THE SINTER BED, BY MEASURING THE SURFACE TEMPERATURE OF THE SINTER BED AFTER IT HAS PASSED THROUGH THE IGNITING FURNACE AND ADJUSTING THE HEAT SOURCE OF THE IGNITING NACE AND OTHER FACTORS, TO CONTROL THE SURFACE TEMPERATURE OF SAID SINTER BED IN THE IGNITING FURNACE.

METHOD FOR SINTERING TO-BE-SINTERED MATERIAL Filed Jan. 6, 1972 Sept. 18, 1973 [KUMI KOGA EIAL 5 Sheets-Sheet 1 UL M G/2%: 2 msmP wwmzamozz SUR TEMP PC) 220 Io3 CALORIES Q Mn I 1 CL Q25 mom FIG.2I

FIG.3

A (PRESENT INVENTION (CONVENTIONAL) METHOD BOT UPPER i MIDDLE OTRECTION OF GRATE DEPTH Sept. 18, 1973 lKUMl KOGA ETA!- 3,759,594

METHOD FOR SINTERING TOBE'SINTERED-MATERIAL Filed Jan. 6, 1972 3 Sheets-Sheet 2 F l G Lfl OPERATING MACH ADDING MACH GAS FLW METER ADJUST ER SUR RADIATION THERMOMETER P 1973 lKUMl KOGA ETTAL 3,759,694

METHOD FOR SINTERING TO-BE-SINIERED MATERIAL Filed Jan. 6, 1972 3 Sheets-Sheet :5

49 TEMP 7 34 fiEiieEfi [f1 INPUE |ND|-, INDICATOR V-A *TEMP I y-- 1 ALARM TRANSDUCER CONT EflmfL nJ 1 J 52 4 fijzys L ifff I DUCER 35 COMPUTER 55\ FLOW CONT 64 at f RATIO FLOW v. AMP CONT XMTR FLOW XMTR RECT ORIFICE E q [FUEL 5 METER 50 55 /62 VELOCITY 25 N/ DAMPER METER United States Patent US. Cl. 75-5 4 Claims ABSTRACT OF THE DISCLOSURE A method for sintering the to-be-sintered material carried on the moving fire grate while a forced draught is given downward thereto, so as to obtain a durable surface of the sinter bed, by measuring the surface temperature of the sinter bed after it has passed through the igniting furnace and adjusting the heat source of the igniting furnace and other factors, to control the surface temperature of said sinter bed in the igniting furnace.

This application is a continuation-in-part of application Ser. No. 846,090, filed July 30, 1969, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates in general to the method for sintering the to-be-sintered material, and more particularly to a method for sintering the to-be-sintered powder material while measuring and controlling the surface temperature of the sinter bed.

Description of the prior art The method which has so far been generally used for sintering such to-be-sintered material as iron ore powder, are mostly equipped with the so-called D.L.s sintering apparatus of bottom suction type and the like apparatus; and these methods are so carried out that the to-be-sintered powder material, a small amount of such fuels as coke (3-5% of the material) and water are mixed in an appropriate proportion, and are charged continuously so as to form a constant depth of the bed; and the fuels contained in the bed of the so charged material are ignited in the igniting furnace of said apparatus, and a forced draught is given from up downward through the suction from the bottom, to burn the fuels such as coke added tosaid to-be-sintered material, as this is moving in the furnace, thereby obtaining such a high temperature between about 1,200" and about 1,300 C. of the material and lumping said powder material by utilization of diffusion-recrystallization of the iron ore powder, and molten slag bondage, etc.

However, according to the above conventional sintering method, after the to-be-sintered material charged on the grate is ignited in an atmosphere of high temperature, it forms the sinter bed, which is moving through said igniting furnace while being sintered and then goes straight out of the furnace, to subject the upper part of the bed of high temperature to sudden cooling with air outside; moreover, because the upper part of the sinter bed is generally not so high heated in the igniting furnace as the middle and the bottom parts of the bed, and because the fuels contained in the upper part of the bed do not burn so well outside the igniting furnace due to cool air, the temperature required for lumping, therefore, is lost from the bed in most cases, before sintering is completed.

Accordingly, the bed sintered by the conventional method of bottom suction type, has different physical strengths by depths, so much so that the upper part of the bed is more than 10% lower in the falling strength index than the middle and the lower parts, that is, the upper part of the sinter bed prepared by said method is very fragile without exceptions.

The so made sinter is cracked into lumps and sorted by a sieve into an appropriate size, and small lumps and powder through the sieve are offgraded, and recycled.

When cracked, most of said upper part of the so made sinter, is liable to get powdered to be off-graded. In order to remove such shortcomings of the conventional sintering methods, there are worked out a method for control of operation of the igniting furnace according to the temperature of atmosphere in the furnace necessary for igniting and burning fuels contained in the surface of the to-be-sintered material; and variety of devices for maintaining constancy of the atmosphere and temperature in the igniting furnace, such as that according to which thermo-couples and inlaid at appropriate positions of the igniting furnace to measure the temperature inside the furnace continuously, and in order to make the temperature constant, the supply of such fuels as gas and heavy oil and the mixing ratio between such fuels and air are adjusted.

However, these method and devices take up, as an object, merely the uniformity of the temperature of the atmosphere in the igniting furnace, and the sinter bed is inevitably subjected to sudden cooling with air outside, these troubles olfsetting the effects of said method and devices and making it quite difiicult to remove the shortcomings of the conventional sintering methods.

SUMMARY OF THE INVENTION The present invention is to solve the above difiiculties of the conventional sintering methods through the improvement of a fragile surface of the sinter to a durable one not by the adjustment of the atmosphere and ternperature of the igniting furnace but by the direct ignition process devised for supplying suflicient calory to the surface of the sinter bed. That is, the present invention is to remove the trouble of fragility of the surface of the sinter by causing high temperature slagging on the surface of the sinter bed in the igniting furnace and other heatkeeping furnaces similar to the foregoing in function (hereafter called the igniting furnace, etc), making the slag bonding wall thicker and the bonding mass greater, thereby giving sufiicient heat to the surface of the sinter bed in the igniting furnace, etc. so that the sinter bed can stand sudden cooling with air when it is Mom of the igniting furnace, etc.

An object of the present invention is to provide, in relation to the sintering method using the so-called D.L.?s sintering apparatus of bottom suction type, a method for sintering the to-be-sintered material stably and easily, thereby producing the sinter having the surface being scarcely different from the middle and the bottom parts in physical strength.

Another object of the present invention is to provide, in relation to the sintering method of bottom suction type, a method for controlling the temperature of the surface of the sinter bed, by measuring the temperature of the surface of the sinter bed just after it has passed through the igniting furnace, and controlling the temperature of the surface of the sinter bed in the igniting furnace on the basis of said measurement.

Another object of the present invention is to provide a method for sintering the to-be-sintered material, thereby preventing the surface of the sintered ore from getting fragile, such fragility constituting a disadvantage of the sinter made by the sintering apparatus of bottom suction type, and producing the sintered ore homogeneously in the direction of depth of the sintering pan.

The present invention is characterized by measuring the temperature of the surface of the sinter bed after it has passed through the igniting furnace, and controlling the supply of fuels, etc. in the igniting furnace on the basis of said measurement.

The method for controlling the temperature of the surface of the sinter bed according to the present invention, consists of such steps in sintering the to-be-sintered material on the moving grate with the supply of downward draught of air made by the suction from the bottom, as measurement of the temperature of the surface of the sinter bed at the outlet of the igniting furnace, etc., conversion to caloric equivalents, of such independent factors related to the temperature of said surface as Strand (fire grade) speed, mixing ratio of coke powder, water content and burnt bed depth ratio, making both the predictive control signal for predicting the lumping temperature of the surface and the corrective control signal for converting to calory equivalents the difference between the predicted lumping temperature of the surface and the measured temperature of the surface, operated with the calory balance used as a medium in the same operation unit, and adjustment of the heat source of the igniting furnace, etc., thereby controlling the temperature of the surfaces of the sinter bed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a graph of the relationship between the temperature of the surface of the sinter bed which has passed through the igniting furnace in the general process of producing the sintered ore and the falling strength index of the surface of the sintered ore in the sintering FIG. 2 shows a graph of the relationship between the above shown surface temperature and calories given to a unit area of the surface of the to-be-sintered material.

FIG. 3 shows one embodiment of the control of the temperature of the surface of the sinter bed according to the present invention, in comparison with an embodiment of the conventional method.

FIG. 4 shows one embodiment of the control of the process of the igniting furnace according to the present invention.

FIG. 5 and FIG. 6 show respectively the section and the plane view of one embodiment of the sintering apparatus used for the method of the present invention.

FIG. 7 shows the controlling apparatus used for the method according to the present invention.

FIG. 8 shows the temperature diagrams of the atmosphere temperature in the igniting furnace and of the surface of the sinter bed respectively when controlled and when not controlled according to the present invention, in comparison the embodiment of the conventional method.

DESCRIPTION OF THE PREFERRED EMBODIMENT Using the figures, effects of the method according to the present invention are explained, as follows:

FIG. 1 shows a graph of the relationship among the temperature at which sintering of the surface of the sinter bed is estimated to have been carried out in the igniting furnace, which bed has just pased through the igniting furnace, the falling strength index of the surface of the sinter bed and the temperature of atmosphere inside the igniting furnace.

It is proven by this figure that according to the conventional method, the relation between the temperature of atmosphere inside the furnace and the temperature of the surface of the sinter bed is very remote (shown by the dotted line), therefore, the control of a forced slagging on the surface of the sinter bed is impossible; and that according to the present invention, the relation between the temperature of the surface of the sinter bed after it has passed through the igniting furnace and the falling strength index is very close (shown by the full line). That is, the figure proves that the control of the surface of the sinter bed is necessary in the igniting furnace.

FIG. 2 shows the relationship between calories given to a unit area of the surface of the sinter bed and its surface temperature. It is proven thereby that the temperature of the surface of the sinter bed is closely related with calory balance and strength of the surface.

FIG. 3 shows a comparison in falling strength indexes between the sinter made according to the present invention and that which was made by the conventional method; and there is a difference in sintering effects between the present invention in which is carried out the control of the surface temperature of the sinter bed (shown by the full line A) and the conventional method (shown by the dotted line B), such difference proves that only a very fragile surface of the sinter is produced by the conventional method.

As a result of the practice of the present invention, the falling strength index of the surface of the sinter was raised by about from that according to the conventional method; the product yield was raised by 2% alike; the difference in strength in the direction of depth of the sinter bed was narrowed; and the so made sinter was homogeneous in physical properties.

Thus, it is confirmed that the lumping of the surface of the sinter bed is made possible by the control of calory balance, for which purpose, it is necessary to continuously measure the surface temperature of the sinter bed at the outlet of the igniting furnace and control the sintering temperautre in the furnace so as to give heat sufficient for lumping the surface of the sinter bed.

In this case, the pattern of change of the surface temperature of the sinter bed is made of the igniting temperature caused by gas or heavy oil flames in the ignition furnace and such calory balance factors as the volume of coke mixed in the to-be-sintered material and the grate moving velocity. That is to say, in case the ignition temperature caused by flames is high, the surface of the sinter bed is subjected to a high heat for a certain time; and in case the volume of coke is great, the burning of the coke takes place actively these conditions making perfect the sintering of the surface of the sinter bed.

The grate moving velocity influences the heat energy furnished by flames to a unit surface area of the sinter bed; if it is made slower, the surface absorbs more heat energy from the flames, thus promoting the lumping of the surface of the sinter bed.

FIG. 4 illustrates one embodiment of the sintering method according to the present invention, which is carried out, as follows; the to-be-sintered material is supplied from the hopper 12 onto the moving grate 1, to form the sinter bed; the to-be-sintered material is ignited in the ignition furnace which is equipped with the burner 3; the surface radiation thermometer 4 (a meter of general type for measuring the surface temperature of the to-be-sintered ore) is set at an appropriate position just outside the outlet of the igniting furnace 2, thereby continuously measuring the surface temperature of the sinter bed.

The difference between the so measured temperature and the temperature for obtaining the intended strength of the surface of the sinter, is detected, and converted by the adjuster 5 into the controlled calory requirement AQ on the other hand, the grate moving velocity is measured by the Strand speed meter (not shown in the figure); and if necessary, such independent variables (W, C, V) as the water content measured by the water content meter (not shown in the figure) and the powder coke mixing ratio measured by the Poid meter (not shown in the figure), and the volume of gas used as a subsidiary variable, are put into the operating machine 7 as input, to calculate the caloric value Q furnished to a unit surface area of the to-be-sintered material; the caloric value Q above is compared with the caloric value Q calculated from the intended temperature of the surface of the sinter bed, to obtain the difference AQ which is put into the adding machine 6 to calculate the sum of AQ -l-AQ the so calculated sum is converted by the gas flow meter 9 into the controlled gas requirement, according to which the gas flow is adjusted by the gas flow adjusting valve 10 of the gas supplying pipe 11.

The abovementioned is the controlling system of the apparatus according to the present invention, and its circuit is formed by the combination of the circuit for predictive control based on independent variables preestablished by using an operating machine and the circuit for feed-back control to correct or difference from the measured surface temperature. In this embodiment, the case where the water content (W), the powder coke mixing ratio (C) and the grate moving speed (V) are used as independent variables, is explained, but the practice of the present invention is not limited to such case.

Also, for the protection of bricks of the igniting furnace, the temperature of the atmosphere inside the furnace, is measured by the thermometer 8, and a maximum is set for the gas flow.

Therefore, when using the method of the present invention, a sinter of homogeneous and better quality can be produced, as compared with the product of the conventional method; moreover, the surface of the so made sinter is less powdery when cracked, such powdering being due to insufficient sintering of the surface; thus, the method of the present invention is effective in preventing the lowering of sinter yield.

FIG. 5 and FIG. 6 show an embodiment of igniting furnace 2. If such igniting furnace as having the structure similar to that of the above furnace 2 is used in the practice of the method of the present invention, sintering can be carried out easily and prefectly. In order to attain the effects to be expected from the present invention, however, the type of the igniting furnace used is not limited to the above furnace 2 or the like, but any type of similar furnace can be used.

The above igniting furnace 2 has a partition wall 13 between itself and a heat preserving furnace 14. Heat preserving furnace 14 consists of a plurality of the heat preserving burners 15 and, from the burners forwardly, a slant ceiling 17 and heat preserving hood 16. Slant ceiling 17 has a great number of small air holes 18. Air supplied from these holes 18 operates to pre-heat the sinter bed, together with flames of burners 15, so as to make smaller the difference in lumping temperature between the surface and the middle and bottom parts of the sinter bed.

The method for controlling the surface temperature of the sinter bed according to the present invention, is explained, as follows.

As mentioned above, in order to make a good lumping of the surface of the sinter bed, the surface temperature should be controlled on the basis of heat, energy furnished to a unit surface area of the sinter bed, that is, calory balance.

FIG. 1 demonstrates a relationship between the surface lump formation degree (the falling strength index) and the surface temperature T of the sinter bed at the exit of the igniting'furnace, which can be expressed by:

Surface lump formation degree=f (T) Combined with the abovementioned Formula 1, this relation develops into the following formula:

Surface lump formation degree=f (Q) where C=mixing ratio of coke powder W=water content V=Strand velocity G=quantity of supplied fuels K =the ratio of the thickness of the burning part to that of the charged material layer in the igniting furnace K =calory generated from fuels in the igniting furnace If the graph shown in FIG. 2 is expressed in the concrete form of function,

where K and P are constants.

The quantity of fuels G to be supplied for generating the surface temperature T so as to attain the desired surface lump formation degree from FIG. 1 or the Formula 1, can be calculated by applying the Formula 6 to the Formula 4, as follows:

The above Formula 7 shows that the amount of fuel to be supplied can be calculated, if the surface temperature T, Strand velocity V, the mixing ratio of coke powder C, the water content W, and the ratio of the thickness of the burning part are known. That is to say, the surface lump formation degree can be controlled by the predictive adjustment of the quantity of to-be-supplied fuels on the basis of the abovementioned factors (the surface temperature T, Strand velocity V, etc.) However, as the above functional relations (1) to (7) have been obtained experimentally, the surface lump formation degree obtained by the control of the quantity of to-be-supplied fules G varies over a substantially wide range, proving that predictive control merely of the quantity of to-besupplied fuels is not sufiicient for obtaining the desired surface lump formation degree.

According to the present invention, the surface lump formation degree can be controlled with high exactness, as there is used a corrective control made by feeding back the surface temperature measured at the exit of the igniting furnace to the predictive control of the quantity of to-be-supplied fuels G The correction AG to be made according to a differential AT (AT: T-T') between the surface temperature T required for the desired surface lump formation degree and the actual surface temperature T' in terms of the quantity of to-be-supplied fuels, is expressed, as follows:

Therefore, the quantity of fuels G to be supplied for obtaining the required surface temperature T, is expressed, as follows:

If the above Formulas 7 and 8 are applied to the Formula 9 the following formulas are deduced:

Through experiments according to the Formula 11 on a commercial scale, there have developed the following values of coefficients and constants:

If these values are applied to the above Formula 11, the following formula is obtained:

In the embodiments of the present invention, all the used instruments, such as desired input indicators, controllers and operation equipments are electrical; therefore, all signals are converted into electric current for subsequent treatment. Thus, the quantity of fuels G supplied according to the above Formula 12, is expressed, as G' as follows:

gas) G is calculated according to the Formula 13 in the following examples:

EXAMPLE 1 In case where the desired surface temperature T=l300- C.; and the actual surface temperature T=1300 C.,

V m./min 3.8 T C 1300 W percent 7 C percent 3.5 K 5/380 Vi ma 15.2 Ti ma 16.0 Wi ma 11.2 Ci ma 11.2

If the above values are applied to the Formula 13,

1 i 50 X11...1l.2) x 3 }=16.267 Ina.

Therefore, the quantity of to-be-supplied fuel gas G corresponding to the above-mentioned G, is G=2542 Nmfi/h.

8 EXAMPLE 2 In case where the desired surface temperature T: 1300" C.; and the actual surface temperature T"=1330 C.

AT=-30 C. ATz'=0.96 ma.

The other conditions are the same as in Example 1.

If the above values are applied to the Formula 13,

l 10.022 ma.

Therefore, the quantity of to-be-supplied fuel gas G corresponding to the above-mentioned G, is G =2503 Nm. /h. This is to say, since the actual surface temperature T was 30 C. higher than the desired surface temperature T, fuel gas G was to be supplied to the igniting burner by 39 Nm. h. less than in Example 1.

As mentioned above, the desired surface lumps formation degree can be obtained by adjusting the quantity of to-be-supplied fuels G through the application to the Formulas 12 and 13 the actual surface temperature T, in addition to the surface temperature T, Strand velocity V, the water content W, the mixing ratio of coke powder C and the ratio of the thickness of burning part K all of which have been so determined as to meet the desired surface lump formation degree.

The following is to explain the above-mentioned con trolling method substantially and concretely by using the instruments shown in FIG. 7.

Powder ore, a to-be-sintered material, is supplied onto belt-conveyor 24 constantly in quantity by a Poid meter 21. The quantity of to-be-supplied fuels is controlled by automatic adjustment of the opening of the gate 23 of the Poid meter 21. Likewise, coke powder, another to-besintered material, is supplied onto the belt-conveyer 24 constantly in quantity by another Poid meter 22. Thus, the powder and the coke powder are to be supplied into a mixer 25 at a certain mixing ratio, which should be predetermined taking into consideration kinds of the powder ore, calory of the coke and other factors, and be put into a desired input indicator 32 as the mixing ratio of coke powder C.

As the mixer 25 is equipped with a nozzle 26, so that a certain quantity of water is supplied through said nozzle 26 into said mixer 25 by adjusting the opening the control valve 27. The water content W is fixedly adjusted by fixing properties of to-be-sintered material, and is put into a desired input indicator 33, together with the mixing ratio of coke powder C.

After mixed in the mixer 25, the powder ore and the coke powder are sent to a hopper 28, and then from said hopper 28 onto a moving grate 29 continuously and constantly in qauntity. Since said grate 29 is moving at a certain speed, the thickness of the layer of the to-besintered material is nearly constant.

The to-be-sintered material supplied on the grate 29 is sent as for as the igniting furnace 30, where the surface of the sinter bed is ignited with a burner 31. The ratio of the thickness of the burning part K that is, the ratio in thickness of the ignited layer against the whole layer in the ignitng furnace, has been determined to an appropriate value, taking into consideration compositions and properties of the to-be-sintered material, thickness of the sinter bed and other factors on the basis of the results of past operations and experiments. Then, the ratio of the thickness of the burning part K has been put into a desired input indicator 34, in the same manner as the abovementioned mixing ratio of coke powder C and said water content W.

Output signals Wt] and or 36 an operation on 1 W'L or) according to the abovementioned Formula 13. Output signal 1 WL Ct] from said subtraction circuit 36 is sent to the multiplication circuit 37 of said computer 35. There is conducted in said circuit 37 an operation on according to the Formula 13, as well as output signal from the desired input indicator 34, into which the ratio of the thickness of the burning part K has been put.

Output signal 1 50 Wt-Ct) K is sent to the addition circuit 38 of said computer 35.

On the other hand, the surface temperature T of the to-be-sintered material ignited in the igniting furnace 30, is measured with a surface radiation pyrometer 45 at the exit of said igniting furnace 30.

Said surface radiation pyrometer 45 is to measure the surface temperature of the sinter bed through the variation of electrical resistance value of the heat receiver according to radiation energy from the surface of the sinter bed concentrated on the receiver by means of a spherical mirror.

The surface temperature T measured by said surface radiation pyrometer 45 is sent, in the form of voltage, to a voltage amplifier 46, so as to be amplified. The so amplified voltage is transformed into direct current T'i by a V-A transducer 47. Signal current Ti is sent to a temperature indicator 49 and also to a temperature controller 48. In said temperature controller 48 has been set the surface temperature T to meet the desired surface lump formation degree. The difference AT (AT=TT') between the so-set surface temperature T and the measured surface temperature T is determined by said temperature controller 48. In actual cases, temperatures are handled after having been converted into electrical values, so it is ATi=Ti=Ti that is put into operation with the temperature controller 48. Output signal [Ti and ATi] from said temperature controller 48 is sent to the addition multiplication circuit 39 of said computer 35 where Item 0.171 (T i-l-ATi) of the Formula 13 is put into operation. Output signal [0.171 (Ti+ATi)] from said operation circuit 39 is sent to the addition circuit 40 of said computer 35, where the constant 9.931 of the Formula 13 is added thereto. Output signal [9.931+0.171 (Ti+ATi)] from the said addition circuit 40 is sent to the addition circuit 38 of said computer 35, where it is added to output signal from said multiplication circuit 37. Then, from said addition circuit 38 is sent output signal to the multiplication circuit 41 of said computer 35.

Strand velocity of to-be-sintered material is detected by a velocity transmitter 50, which is a tachometer of generator type for the detection of the rotation speed of Strandwheel.

Output signal from said velocity transmitter 50 is sent, in the form of voltage, to a rectifier 51 to be transformed into direct current, and then sent to a V-A transducer 52 to be converted, into electric current. Output signal [Vi] from said V-A transducer 52 is sent to a Strand velocity alarm 53 and also to the multiplication circuit 41 of said computer 35.

In said multiplication circuit 41, input signal from said addition circuit 38 and input signal [Vi] from said V-A transducer 52 are put into multiplication; and from said multiplication circuit 41 is sent output signal [G'] expressed with the Formula 13 to a flow controller 55.

The burner 31 of said igniting furnace 30 is connected with a pipe 56 for transporting such fuels as coke oven gas and heavy oil and a pipe 61 for supply air for burning such fuels.

Output from said flow controller is sent to the electric oil pressure actuator 58 of a. fiow control valve 57 mounted on said fuel pipe 56. Said flow control valve 57, opens and closes in response to said output signal, so as to control the supply to the igniting furnace of fuels to an appropriate amount, thereby attaining the projected surface temperature, and finally the desired surface lump formation degree. Downstream of said flow control valve 57 is equipped an orifice meter 59. The pressure difference detected by said orifice meter 59 is converted by a flow transmitter 60 into electric current.

Output signal from said flow transmitter 60 is fed back to said flow controller 55, so that fuels supplied to the burner 31 of the igniting furnace is controlled at a high exactness.

The pipe 61 for supply air for burning fuels is equipped with an orifice meter 62. The pressure difference of said orifice meter 62 is converted by a flow transmitter 63 into electric current. Output signal from said flow transmitter 63 is sent to a ratio controller 64. Input signal of the flow of fuels is sent from the flow transmitter 60 to said ratio controller 64. Then, in said ratio controller 64 is determined an appropriate amount of air for the flow of fuels. Output signal from said ratio controller 64 is sent to the electric-oil pressure actuator 66 of a damper 65. Said damper 65 opens and closes in response to said output signal, thereby supplying an appropriate amount of air for the combustion of fuels.

Reference is made to the abovementioned Formula 9, according to which the quantity of to-be-supplied fuels G calculated by using the mixing ratio of coke powder, the water content Strand velocity, the ratio of thickness of the burning part of the layer against the whole layer of the sinter bed and the calory generated from fuels, and the quantity of to-be-supplied fuels as corrected by the measured surface temperature are summed up after such adjustment with rated weights of respective quantities as to make them equivalent in terms of the effect on the surface lump formation degree; in other words, such rated weights represent respective effects of the calculated quantity for control G and the feed-back quantity for control AG on the surface lump formation degree.

Taking the abovementioned rated weights into consideration, said Formula 9 can be expressed in the following rnanner, too,

G =aG +IBAG (9) where a and ,8 represent rated weights; and a+fi=1.

For instance, if 18:0, the control of temperature in this case is a completely predictive control. The operation of fuels G and the quantity of to-be-supplied fuels as corrected by the measured surface temperature AG are summed up after having been adjusted with rated weights to be made equivalent, the surface temperature, that is, the surface lump formation degree of to-be-sintered material, is controlled with the least variance.

Table 1 shows one example of such results as mentioned above.

TABLE 1 Control on Without Control 50% prediccontrol on 100% tive and 50% (conventionpredictive feed-back al method) control control Projected surface temp, C 1, 050 1, 050 Measured surface temp, C 1, 066 1, 045 1, 047 Variance of surface temp, 0.

(2X standard deviation) 116 44 8 Variance of surface lump formation degree (2X standard deviation)..- 3. 32 0. 88 0. 16

The result of the operation of the controlling apparatus according to the present invention: FIG. 3 shows one embodiment of the control of the surface temperature of the sinter bed using gas flow in the above controlling apparatus operating on a plant scale. As a result of this experiment, the falling strength index on the surface was found to be raised by about 50%, and the yield of product by about 2% More important is the fact that physical properties of the sintered ore to be charged into the blast furnace, has become less variable and almost homogeneous in the direction of depth and in a time series.

FIG. 8 shows the temperature diagrams of the surface of the sinter bed and of the atmosphere in the igniting furnace when controlled according to the present invention, in comparison with such diagrams obtained by the conventional method which provides no control.

The diagram A shows the surface temperature of the sinter bed in operations by the conventional method, the diagram B shows the temperature of atmosphere in the igniting furnace in operations by the conventional method, the diagram C shows the temperature of atmosphere in the igniting furnace in operations according to the present invention, the diagram D shows the surface temperature of the sinted bed in operations according to the present invention.

What we claim is:

1. In a method of sintering to-be-sintered powder material by adding thereto fuels, such as coke, of small quantity and an appropriate amount of water, charging the so-made mixture in a predetermined thickness onto the moving grate of a sintering apparatus, continuously igniting said fuels contained in the charged material layer with the igniting furnace of said sintering apparatus, and drawing air by suction passing through said grate from above said grate toward below said grate, thereby causing combustion of said fuels contained in the charged material layer to generate heat of a high temperature for continuously sintering said charged material layer;

the improvement comprising:

controlling the quantity of fuels to be supplied to said igniting furnace so as to have sufficient calories held in the surface part of the sinter bed in the igniting furnace for making as small as possible the difference in temperature between the upper part and the lower part of the sinter bed, thereby making nearly uniform the lump formation of the so-sintered material throughout said sinter bed from the upper part thereof to the lower part thereof; said controlling comprising the steps of initially calculating the quantity of fuels to be supplied to said igniting furnace on the basis of the mixing ratio of fuels and water, the ratio of thickness of the burning part to that of the charged material layer in the igniting furnace and strand velocity; measuring the surface temperature of the sinter bed at the exit of said igniting furnace; calculating the difference betwen the so-measured surface temperature and the surface temperature required for lump formation; correcting the above-calculated quantity of to-be-supplied fuels according to said difference of temperatuure; and adjusting the quantity of fuels to be supplied to said igniting furnace by using, as an input, the corrected quantity of to-besupplied fuels.

2. The method claimed in claim 1, wherein the calculation of the quantity of fuels to be supplied into said igniting furnace and the correction of the calculated quantity of to-be-supplied fuels by means of the abovementioned difference of surface temperatures, are carried out converting the mixing ratio of the fuels and water. Strand velocity, the ratio of the thickness of the burning part to that of the charged material layer in the igniting-furnace and the difference of the surface temperature into calorific value per unit time in supplying to the igniting furnace.

3. The method claimed in claim 1, wherein the sum of the initially calculated quantity of to-be-supplied fuels and the quantity of to-be-supplied fuels as corrected therefrom by the measured surface temperature, these quantities having been so adjusted with rated weights as to be made equivalent in terms of the effect on the surface lump formation degree, is used as the quantity of fuels to be supplied into the igniting furnace.

4. In an apparatus for sintering to-be-sintered material by continuously igniting said material charged in a predetermined thickness onto the moving grate of an igniting furnace of a sintering apparatus, the improvement comprising a heat preserving furnace adjacent said igniting furnace with a partition wall therebetween, said heat preserving furnace including a plurality of heat preserving burners, a ceiling slanting downwardly toward said material in the direction of movement of said material, said ceiling having a plurality of small holes for the introduction of air therein, and a heat preserving cover, said heat preserving burners heating the surface of the sintering bed of said material after the exit thereof from said furnace so as to make as small as possible the difference in temperatures between the upper and the lower parts of said sintering bed, whereby a drop of the oxygen partial pressure in said heat preserving furnace is corrected by air supplied through said air introduction holes provided in said ceiling.

References Cited UNITED STATES PATENTS 3,194,546 7/1965 Schuerger et al 263-28 X 3,275,431 9/1966 Sawada 266-21 X 3,211,441 10/1965 Mikakawa 266-21 2,668,042 2/ 1954 Meyer et al 263-53 R 2,148,052 2/1939 Ahlmann 263-53 R JOHN J. CAMBY, Primary Examiner US. Cl. X.R. 432-7 

